Detergent compositions for use in automatic dishwashing equipment have long contained a bleaching agent to operate in the relatively severe conditions of such equipment. High temperatures conditions and highly alkaline solutions of detergent materials effectively clean dishes and silverware by hydraulic action. In such systems bleach concentrations as well as detergent concentrations can be tolerated at higher levels than those levels employed with hand washing operations for obvious reasons. There has long been prepared granular or powder compositions designed for automatic dishwasher use conveniently placed in the compartment of the automatic dishwasher and released at the appropriate time by the mechanism of the mechanical dishwasher. However, modern marketing trends has shown that it is becoming more desirable to prepare liquid compositions rather then powder compositions for use in such apparatus. Therefore, stable formulations in liquid form such as slurries are being sought which can safely and conveniently be employed in place of previously employed powder compositions.
Liquid automatic dishwasher cleaning compositions present new problems and increased potential for consequences of misuse not previously encountered with powder compositions. For example, the bleaching agent in powder compositions spilled upon textile material can easily be removed without damage provided no liquid is available for the bleaching agent to become activated. Simple brushing will provide removal of the detergent composition containing the bleaching agent without serious danger of dye damage resulting from the bleach which is present, as previously noted, in relatively high concentration. However, should a slurry composition be misused or spilled upon textile material, it will immediately allow bleach activity and severe dye damage to occur, not allowing an opportunity for removal before such damage occurs.
Liquid detergent formulations for automatic dishwasher use has exacerbated another problem known in the art and previously controlled. Such problem is metal corrosion. Previously, metal corrosion has been effectively dealt with by incorporating a metal corrosion inhibitor in the composition, such inhibitors being generally sodium silicate or clays. Sodium silicate use as a metal corrosion inhibitor was known as for example in U.S. Pat. No. 3,468,803 to Knapp et al which discloses powder formulations useful in automatic dishwasher apparatus. Knapp et al recognize that metal corrosion inhibition satisfactory for protection of metal portions of the dishwashing apparatus was obtained by such corrosion inhibitors as sodium silicate but in liquid formulations such material is inadequate, particularly for inhibition of corrosion of precious metals such as silver. Knapp et al teach that silver corrosion inhibition is achieved by incorporation of cyanuric acid or a salt thereof in the liquid formulation. Also, German published application DE3,325,503A discloses liquid or thixotropic detergent formulations for automatic dishwasher apparatus wherein sodium silicate is employed to inhibit corrosion of metals and to protect china.
The incorporation of a bleaching agent in liquid formulations for automatic dishwasher use greatly increases the risk of damage because of the concentrated form which these formulations must take. Initial entry into the dishwasher apparatus of the liquid formulation can damage metal quickly before dilution occurs. Even in diluted form corrosion of metals such as silver remains a problem for liquid detergent formulations for automatic dishwashers.
In spite of the dangers of spillage and other misuse, consumers have perceived that liquid automatic dishwasher liquids are more desirable powder formulations because of their ease in handling and recognized quicker dissolution in the automatic dishwasher. Most consumers have witnessed powders in automatic dishwashers that leave a gritty residue or are found in a solid lump which did not dissolve well during the wash cycle. There is therefore desired an automatic dishwasher liquid detergent formulation which overcomes the above noted deficiencies.